The present invention relates to a hand-held working tool, especially a motor chainsaw etc., comprising an internal combustion engine arranged in a housing and having a crankshaft for driving a tool and a fan wheel. The fan wheel is arranged in a fan housing and conveys through an air inlet cooling air to the internal combustion engine. Combustion air is axially guided through an outlet opening in the housing bottom via a combustion air channel to the air filter of the internal combustion engine.
U.S. Pat. No. 3,994,076 discloses a motor chainsaw in which an air-cooled internal combustion engine is arranged in a housing. The crankshaft of the internal combustion engine supports at one end the drive member for the tool, i.e., a saw chain circulating on a guide bar. The other end drives a fan wheel which is arranged within a fan housing and takes in cooling air through an air inlet for supplying the cooling air to the combustion engine. A portion of the intake air of the fan wheel is guided as combustion air to the air filter of the internal combustion engine. The combustion air is supplied via an outlet opening, provided in the bottom of the fan housing and covered by the fan wheel, in the axial direction and is guided via a combustion air channel to the air filter. The known arrangement with axially directed air removed from a chamber that is delimited by the fan housing bottom and the end face of the fan wheel and that contains centrifuged suction air will provide substantially dust-free combustion air to the dirt chamber of the air filter.
The outlet opening in the known device is arranged centrally within the bottom of the fan housing, i.e., adjacent to the crankshaft bearing within the crankshaft housing of the internal combustion engine. The combustion air channel connected to the outlet opening must have over its entire length a sufficiently large flow cross-section for supplying the required combustion air amount. In the known arrangement the combustion air channel connection between the outlet opening at the housing bottom and the air filter as well as, in the flow direction, the connection downstream to the carburetor of the internal combustion engine requires great constructive expenditures. The complicated channel design of the combustion air channel increases the size of the working tool so that its ease of manipulation and operating comfort are impeded.
It is therefore an object of the present invention to provide a working tool of the aforementioned kind with which a simple guiding of clean combustion air in combination with a compact design of the hand-held working tool is possible.